Impact sensitive top fuze



June 1965 e. H. s. HOLMSTRQM IMPACT SENSITIVE TOP FUZE Filed July 26, 1962 :Illll aIII I u Ill I I I I 1/ United States Patent This invention relates to a highly sensitive top fuze for rotating shells as well as for non-rotating shells, and more particularly to shells having a shaped charge. The invention has for its primary object to insure a safe and rapid ignition upon frontal as well as upon oblique impact of such a shell with a target and to reduce the dependency of the ignition on the angle of impact.

It is well known that, if a fuze construction contains a firing pin, a considerably delayed ignition is obtained due to the, action of the firing pin by striking the primer charge and efforts have been made to reduce such a delay. Moreover, as far as modern shells are concerned, especially those having-a shaped charge, it is desirable that ignition should occur upon oblique contacts. In this connection, a short time of ignition is desirable since a penetrating effect is otherwise difficult to obtain. fuzes for ignition upon oblique impacts, however, are generally based upon the use of firing pins or solid bodies, which upon impact have to be put in motion or moved aside, thus causing a delayed ignition.

In order to reduce the time of ignition, pinless fuzes have been proposed, in the top of which an impact sensitive primer is arranged and being included merely in a thin-walled casing. Hitherto known fuzes of this kind however, are able to function only upon frontal contacts or close to frontal impacts.

In trying to modify such fuze constructions in order to have them fuction on frontal as well as on oblique impacts, it has proved to be difficult to secure a rapid function of such a fuze without introducing other drawbacks.

Existing Making the impact-sensitive primer accessible under would also result in economical and manufacturing inconvenience. Spreading the primer charge in the form of a thin layer along the inside of the side wall of the fuze body, near the top of it, would cause difiiculties in securing a safe and simple connection with an auxiliary charge and a booster charge behind the latter, such a booster charge being used in connection with a device for making the fuze bore and trajectory safe. In both cases it would be difficult to keep the fuze small and light in weight.

The present invention is based on the well known principle of an impact-sensitive detonating cap being arranged in the top of the fuze, but constitutes a solution of the fuze problem which will eliminate the drawbacks mentioned above. The invention primarily resides in the detonating cap forming a double-walled tubular casing, a part of which protrudes in front of the fuze body, said casing or at least the protruding part of it, being easily deformable, and including an impact-sensitive primer charge and having an auxiliary charge located behind the primer charge.

The statement that the casing is easily deformable implies that its walls should be so thin and also so soft as too be easily impressed, or so brittle as to be shattered into a number of small pieces upon the impact, which pieces penetrate the primer charge. The ignition 3,19%,222 Patented June 22, 1965 of the primer charge is due to several causes. It is probably caused by the charge being compressed between the outer and inner wall of the casing and/or being ground against them, whereby an improved effect is obtained due to the rupture of the casing e.g. in the section of the transition to a strengthened part of its wall, which part 7 might be either a thickened wall or a supporting wall. It has however been proved that a layer of the primer charge should be thin if short time of ignition is to be obtained. That is, the distance between the outer and inner walls of the casing should be small. This indicates that the inner wall of the casing acts as an anvil upon impact. Such an anvil effect is an explanation of the fact that the time of ignition is shortened if at least the free portion of the inner wall, abutting against the layer of the primer charge, is made thicker. It has resulted that the thickness of this wall portion need not essentially exceed the double thickness of the outer wall of the casing for the improvement, attainable in this way, to be utilized.

The increased thickness of the inner wall of the casing can be produced in a simple manner by combining an inner tube with an outer tube, with the latter having a flanged bottom pressed around the front end of the inner tube, so as to form a collar on the inside of the inner tube and in a suitable manner joining and tighten ing it to said inside.

In a fuze of the present invention the detonating cap may extend rearwardly to a substantial extent and it may be provided with so powerful an auxiliary charge, that the charge will directly detonate a bursting charge of a shell used with the fuze. Alternately, the fuze may be provided with a booster, arranged to be set ofi by the explosion of the auxiliary charge of the detonating cap. Usually the fuze is required to contain a device for mak ing it bore and trajectory safe. Accordingly, the present invention also refers to a fuze construction having such a device. In such construction the detonating cap has a limited extension rearwardly so as to be embraced only by the forward portion of the fuze body, the rear portion of which contains a booster, which is slidable within the fuze body and, in a well known manner, provided with a propelling coil spring and a safety device, the booster being so arranged, that the forward end of its charge is embraced by the rear portion of the detonating cap, when the booster is brought to its forward position but shall be shielded from it by the forward end of the booster casing when the booster is brought to its rearward position. This arrangement is an application of a well known principle of co-operation between a front charge and a rear charge of a fuze. Considering a fuze of the present invention, it is however particularly favorable to apply this principle, owing to the detonator having a tubular shape. By employing a safety device of this kind, no departures are required from giving the detonator a shape suitable for its main purpose.

It is often desirable that the fuze be closed, particularly when it contains a safety device. In a fuze of the present invention this is efiected by a closing wall, transversely placed in the casing of the detonating cap at some distance from its front end. In a preferred form the casing of the detonating cap consists of an inner tube, and an outer tube haying a bottom at its front end, such bottom being pressed into the end of the inner tube, so as to make its inside wall thicker as well as to form a desired closing wall. Such a closing wall acts as a sup porting wall for the inner wall of the detonating cap, promoting its function of ignition and, when the above mentioned safety device is employed, this closing wall will cause the forward movement of the slidable booster to be dampened by air between it and the front end of the booster. This dampening effect can be adjusted to the required time of bore safety by providing the front portion of the booster casing with escape channels or a suflicient allowance in relation to the inner wall of the casing of the detonating cap. To meet demands for long periods of trajectory safety on the other hand, a packing means can be arranged between the booster casing and the casing of the detonating cap, such packing means being in the form of a packing ring or inserted silicon grease. In order to obtain a safe handling of the fuze, the portion of the detonating cap that is unprotected by the fuze body can be covered by a protecting hood, preferably being detachable by being thrown off. In this connection it is preferable to employ the same blocking means as those a ting upon the booster casing.

In a preferred embodiment of the present invention, the detonating cap is slidably arranged in the fuze body, that is, mounted in a sleeve, in turn being slidable in the fuze body with such an axial motion margin that an essential portion of the fuze body will be blasted away before the slidable unit has been moved to its rearward position. By this arrangement the transferring of a shock wave to the fuze body will be delayed, such a shock wave, transferred from the fuze body to the shell, being able to cause damage to vital parts of the shell, namely, damage to a shaped charge, included therein.

Still further objects, features and advantages of the invention will become apparent from the following description taken in connection with the accompanying drawing, wherein FIG. 1 is a longitudinal sectional view of a fuze in which the present invention is embodied, and FIGS. 2 to 4 are respectively longitudinal sectional views of alternative forms of the fuze as constructed according to the present invention.

Referring to the drawing and more particularly to FIG. 1, a fuze is therein shown, the same including a tubular fuze body 8, having a bottom screw plug 26, an impact-sensitive detonating cap generally indicated at 3 containing charges 2, 4, located in the forward end portion of the fuze body, and a booster disposed within the rear portion of the fuze body 8. The front portion 11 and the rear portion 21 of the booster are kept together by a bushing 14.

The detonating cap 3 consists of a double-walled tubular casing 3a, the rear end of which is closed by a bottom 5. The rear portion of the detonating cap is embraced by the fuze body 8, but its forward portion pro trudes in front of the fuze body. In its front portion the detonating cap contains an impact-sensitive primer charge 2 extending rearwardiy to about the front end of the fuze body. The primer charge consists of lead azide and a minor portion of a sensitizing ingredient such as Tetrazen. The detonating cap also includes an auxiliary charge 4, located behind the primer charge, and consisting of one or more layers of sensitive explosives, such as tetryl. The casing 3a of the detonating cap 3 consists of a hardened aluminum alloy of good ductibility and strength. It preferably has a thin wall thickness so as to be deformed by slight impacts, the wall thickness being adapted to a required degree of sensitivity, so that ignition will be avoided upon impact with slight obstacles such as bushes. The distance between the walls of the casing 3a is short and as a result the layer of the enclosed primer charge is thin, a good ignition result being obtained with a layer thickness of 1.5 mm. By giving the same dimensions and shape to the portion of the casing that encloses the less sensitive auxiliary charge 4, the manufacture of the casing 3a will be simplified as well as the connection between the casing and a rear booster for transferring the ignition to the bursting charge of the shell used with the fuze.

The booster ill, 21 is slidably arranged in the rear portion of the fuze and has a transition charge It! in its forward portion 11 and an auxiliary charge in its rear portion, both charges consisting of relatively insensitive high explosives. The forward end of the booster casing 11 has a thick cylindrical wall 7. When the booster is brought to its forward position, this wall extends so far into the detonating cap, that the charge 1% of the booster is partly embraced by the auxiliary charge 4 of the detonating cap enabling it to be ignited from the latter, the fuze being thus armed. In the position of the booster, as shown in FIG. 1, the front wall 7 is behind the auxiliary charge 4 of the detonating cap, thereby shielding the latter from the transition charge 10 of the booster. in this condition of the safety arrangement, the fuze will be unarmed.

The fuze is provided with a guide bushing 24 embracing the booster casing II, 21 and at its forward end 9 it also embraces the rear end of the detonating cap to which it is secured. The rear end of the guide bushing houses a coil spring 22 arranged to move the booster casing 11, 21 forward. The safety mechanism disposed within the fuze is adapted to operate according to a well known principle. In the arrangement shown in FIG. 1, it comprises blocking balls 16, a conical shoulder 17 on the outside of the bushing 14 and a blocking sleeve 18, slidable within the fuze body, said sleeve having an inwardly-directed flange 18a on its forward end and having a circumferential groove on its outside housing a friction spring 19. The fuze body 8 has a circumferential shoulder 8a on its inner side, said shoulder constituting a stop face which co-operates with the forward end of the blocking sleeve 18. When the blocking sleeve 18 is in its forward position as shown by the disclosure of FIG. 1, its inwardly directed flange 18a will prevent the blocking balls 16, and as a consequence the booster casing 11, 21 as well as the bushing 24 from moving forwardly. Simultaneously the blocking balls 16 constitute stop members behind said flange 18a as to prevent the blocking sleeve 13 from moving backwardly, as long as the blocking balls 16 are forced against the inner side of the blocking sleeve 18 by the conical shoulder 17 of the bushing 14. The central portion of the guide bushing 24 is provided with axially-extending apertures 13 for the blocking balls 16 and the rear portion of the guide bushing is formed with a flange portion, the frontal surface of which constitutes a stop face co-opcrating with the rear end surface of the blocking sleeve 18.

The rear mouth opening of the fuze is closed by a thin disk 25. The fuze is provided with a protective hood I at its forward end embracing the free portion of the detonating cap. The protective hood is connected with a holding sleeve 12 by means of a lock device 6. The rear portion of the holding sleeve 12 is provided with apertures 15, so as to be held by the blocking balls, 16.

In the embodiment shown in FIG. 1, the same safety device is used to keep the booster casing 11, 21, the protective hood I and the detonating cap 3 locked to the fuze body 8 before the firing of the shell and to release such members after the shell has been fired.

The operation of the safety device is as follows: Upon firing, set-back forces, acting on the fuze, immediately cause the booster casing 11, 21 and then, with some delay owing to the blocking effect of the blocking balls 16, the blocking sleeve 18 to be moved backwardly. The blocking balls 16 are forced by the flange 18a of the blocking sleeve 18 against the booster casing 11, 21 above the conical shoulder 17 of the bushing 14, without entirely leaving the apertures 15 of the holding sleeve 12. By the retardation of the fuze in the trajectory owing to the air resistance of the shell and by aid of the coil spring 22 the booster casing 11, 21 is forced ahead. The blocking balls 15 are forced'outward back in full engagement with the apertures 15 of the holding sleeve 12 by the forward portion of the bushing 14.

The blocking balls, now supported against the conical shoulder 17 of the bushing 14 are brought forwardly together with the booster casing, thereby being conveyed in the axial apertures 13 of the bushing 24. Then the booster casing is not prevented from reaching its forward position in which it is partly embraced by the detonating cap. The blocking balls engage the holding sleeve 12, which consequently is forced ahead, taking the protective hood 1 with it.

Before the shell is fired, the bushing 24 is held blocked in its rear position by the blocking balls 16, until the booster casing 1-1, 21 and the blocking sleeve 18 have moved rearwardly, so as to release the blocking balls from their blocking condition. After that the bushing 24 is prevented from forward movement merely by the action of the coil spring 22, the forward end of which presses against the rear end surface of the bushing 14. This action, however will cease in a very short time after the booster casing 11, 21 together with the bushing 14 has begun to move forward. Consequently the guide bushing 24 with little delay will move forward owing to its inertia, taking along with it the detonating cap 3, attached to it. Its motion however, is limited by the front surface 23 of the rear flange portion of the guide bushing 24 striking against the rear end surface of the blocking sleeve 18, which sleeve is slidable only a short distance, being stopped by the-shoulder 3a of the fuze body. The guide bushing 24 being slidable within a small axial allowance, that is 3.5 mm. prevents a rigid connection between the fuze body 8 and the detonating cap 3. The process of ignition will be accomplished before the guide bushing with the detonating cap 3 is brought into contact with thetube bottom 26 of the fuze thereby preventing a shock wave from being transferred to the fuze body.

In FIGS. 2 to 4 only the front portion of the fuze is shown, on an enlarged scale. The detonating cap 3, its primer charge 2 and its auxiliary charge 4 are also arranged in the fuze body 8 as previously described. The holding sleeve 11 is however, shown in its forward position and th protective hood is presumed to have been thrown off.

In the fuze illustrated in FIG. 2, the forward portion of the inner wall of the casing 3a is twice as thick as the other wall portions of the casing and extends to about one-half the length of the layer of the primer charge 2.

In the embodiment illustrated in FIG. 3, the corresponding thicker wall portion has been created by the casing 3 being composed of an inner tube 28 and a concentrically arranged outer tube 25 the latter having a bottom flange, a portion of which is downturned by pressure into the inner tube and joined to the inside thereof to thereby form a collar inside of the inner tube.

The fuze shown in FIG. 4 represents a development of that shown in FIG. 3. The outer tube is formed with a bottom wall without any central aperture and said bottom wall is pressed into the end of the inner tube, so as to form a collar 30, inside of the forward portion of the inner tube 28, as well as a closing wall 31. This figure also shows a portion of the booster safety device of the kind described above, the casing of that booster being in its forward position and the fuze thereby being armed. The closing wall 3 1 is at such a distance from the end of the fuze that the front end 7 of the booster casing 11 just reaches this wall. The closing wall 31 is of particular significance in fuzes having a safety device of this kind. The air enclosed between this wall and the end wall 7 can be utilized for dampening the forward movement of the booster casing 11. As the booster casing has a certain allowance in the fuze, a too-hard dampening effect will be prevented, that is if the all-owance is properly adjusted and if necessary, supplemented with external longitudinal grooves, the dampening effeet can be adapted to the required time of trajectory safety.

A closing wall can be arranged in other ways than is shown in FIG. 4 and it is not necessary to make'the inner wall of the detonating cap thicker at its front end at the same time. The closing wall should, however, be placed at some distance from the end of the detonating cap, preferably near its middle plane, so as to be able to co-operate with an existing booster safety device.

Having thus described embodiments of the invention, it is obvious that the same is not to be restricted thereto, but is broad enough to cover all structures coming with in the scope of the annexed claims.

What I claim is:

1. An impact-sensitive top fuze having a body pro vided with a detonating cap in it, said cap consisting of an annular casing protruding from the fuze body, the protruding portion of the casing being readily deformable, said c-asing having an inner and an outer tubular wall, which walls define an annular space between them, an annular wall at each end of the casing for closing said space, an impact-sensitive primer charge occupying the forward portion of said space, and an auxiliary charge occupying the remaining portion of said space.

2. An impact-sensitive top fuze as provided for in claim 1, wherein the forward portion of the inner tubular wall of the casing has a considerably greater 'thick ness than other wall portions of said casing, the length of said thickened wall portion not exceeding the length of the primer charge.

3. An impact-sensitive top fuze as provided for in claim 1, wherein the casing is partly composed of an inner tube and partly composed of an outer tube, the outer tube being provided with a bottom flange extended into the forward end of the inner tube to provide a collar around the same, said collar being secured to the Wall of the inner tube.

4. An impact-sensitive top fuze as provided for in claim 1, wherein the casing defines a passage within it and a transverse wall is disposed within the passage through the annular casing in a plane between the ends of the primary charge, thereby closing said passage.

5. An impact-sensitive top fuze as provided for in claim 1, wherein the casing is composed of an inner tube and an outer tube, said outer tube being shaped with an inwardly-directed cup at its forward end, said cup fitting within the forward end of the inner tube to thereby form a collar around the inside of the inner tube at its forward end and to provide a transverse closing wall located to the rear of said forward end.

6. An impact-sensitive top fuze having a body and an annular impact-sensitive detonating cap protruding from the fuze body, the rear portion of said annular cap being disposed in the forward portion of the fuze body, a booster slidably arranged in the rear portion of the fuze body, said booster being biased forwardly by a propelling coil spring blocking means preventing forward movement of the booster, inertia-actuated means co-operating with the blocking mean-s for bringing the blocking means out of blocking position upon firing,

the forward end of the booster charge being embraced by the rear portion of the annular detonating cap, when the booster is moved to its forward position, the booster having a charge and having a for-ward end wall shielding its charge from the rear portion of the annular detonating cap when the booster is rearwardly disposed.

7. An impact-sensitive top fuze as provided for in claim 1, wherein the detonating cap is slidably arranged within the fuze body with such a margin of axial movement that a forward portion of the fuze body will be blasted away before the detonating cap has moved to its rearmost position.

8. An impact-sensitive top fuze as provided for in claim 7, wherein there is a guide bushing axially slidable in the fuze body the detonating cap being mounted in and is fixed to the forward end of said guide bushing, the fuze body having a rear-end closure, the guide bushing resting against said closure when in its rearmost 3,190, "5" position, the guide bushing having a portion with a forwardly-directed stop face, and the fuze body having an element arranged in the path of motion of said forwardly directed stop face so as to keep the forward movement of the bushing within a desired axial allowance. 5

References Cited by the Examiner UNITED STATES PATENTS 1,455,741 5/23 Wennerstrom 10278 4/55 Moseman 102-78 3/56 Brandt 10278 X 2/57 Migliaccio 10273 X 4/60 Henning et a1 10238 X FOREIGN PATENTS 4/49 Great Britain.

SAMUEL FEINBERG, Primary Examiner. 

1. AN IMPACT-SENSITIVE TOP FUZE HAVING A BODY PROVIDED WITH A DETONATING CAP IN IT, SAID CAP CONSISTING OF AN ANNULAR CASING PROTRUDING FROM THE FUSE BODY, THE PROTRUDING PORTION OF THE CASING BEING READILY DEFORMABLE, SAID CASING HAVING AN INNER AND AN OUTER TUBULAR WALL, WHICH WALLS DEFINE AN ANNULAR SPACE BETWEEN THEM, AN ANNULAR WALL AT EACH END OF THE CASING FOR CLOSING SAID SPACE, AN IMPACT-SENSITIVE PRIMER CHARGE OCCUPYING THE FORWARD PORTION OF SAID SPACE, AND IN AUXILIARY CHARGE OCCUPYING THE REMAINING PORTION OF SAID SPACE. 